The invention relates to a method for the treatment, and more particularly the catalytic treatment, of the exhaust gas of IC engines and more especially of motor vehicle engines, in the case of which the gases resulting from combustion are caused to flow through a converter, and also to an apparatus for performing the method.
When an IC engine is started from cold large quantities of pollutants are emitted in the exhaust gas. It is known to employ a converter, which is placed downstream from the exhaust gas outlet of the engine, in order to reduce the emission of pollutants, the most well known types of converter being those utilized in the case of gasoline engines and referred to as catalytic converters. In the case of diesel engines as well converters are employed in order for instance to reduce the level of CO, unburnt hydrocarbons, and/or soot or solid particles in the exhaust gas. The present invention is more particularly described in relation to converters for gasoline engines, but however the same sort of problems occurs in the case of other converters for the treatment of exhaust gas of IC engines generally.
Such converters demand a certain minimum temperature of the reaction partners in order to develop their effect. Until the reactants have reached this minimum temperature the pollutants are left off into the environment unconverted.
Conventional three-way catalytic converters comprise catalytic material for the oxidation of CO and unburned hydrocarbons, and furthermore for instance for the reduction of NO.sub.x. Owing to the time taken for the catalytic converter to reach its operational temperature certain pollutants, and more particularly CO and unburned hydrocarbons will be emitted, while substantial emission of NO.sub.x only occurs when the conventional operational temperatures are attained.
In order to diminish this delay or lag in the coming into operation of the catalytic converter a large number of at least theoretical possibilities have been evolved, as for instance the electrical heating of the exhaust gas before the same reaches the catalytic converter, the additional heating of the catalytic converter or the keeping of the catalytic converter in the heated condition by thermal insulation.
Although some of these measures have led to substantial improvements in the situation, there is still the basic defect that when starting up from cold and in the first three minutes of warming up the engine produces very high emission peak values as regards unburned hydrocarbons and carbon monoxide, while during this time the catalytic converter is still not able to act. The two conditions are connected with the fact that both in the engine and also in the converter the optimum operational temperatures have not yet been reached.